Length of a tack weld

Date 01-30-2002 03:05

I have not found a reference in the D1.1 or the D1.5 on the length of a tack weld. The only reference to length (short) is on an intermittent weld at 40mm. At this time the only rule I use is to preheat per Code before you tack, make it smaller in leg length than the final weld, make it just large enough not to crack during the final weld, grind it down as to not effect the final weld profile, never make the tack at the beginning or the end of the final permenant weld and taper the ends of the tack to ensure a complete remelt of the base metal during the final weld. Is there any other reference I can check out to resolve this. The D1.5 would be the target code I use. I have had other inspectors want a 1 1/2" long "tack" to hold stiffeners in place before the final weld. I know they are looking for a minimum amount of heat input to keep the HAZ from cooling too fast. Anyone have any insight and even better a published reference? THANKS in advance James

By dong won oh (*)

Date 01-31-2002 05:33

I used to work for shipbuilding in Korea.
Classification specifies 30mm min. for mild steel(60ksi tensile) and 50mm min. for high tensile steel(70ksi tensile).
I have experienced cold cracking(underbead cracking) in the tack weld for back strip of narrow gap welding.
The reason was fast cooling due to very short tack weld.
Seoul, Dong Won Oh

By CHGuilford (****)

Date 01-31-2002 15:54

James,
The "AASHTO Commentary on the ANSI/AASHTO/AWS D1.5-88 Bridge Welding Code" might give you more insight on the matter. There isn't really a lot said on the subject, so usually it becomes a matter of who's opinion carries the most weight.
CHGuilford

By pdweldor (*)

Date 02-01-2002 18:00

AWS A3.0 Standard Welding Terms and Definitions states that a tack weld is "a weld made to hold the parts of a weldment in proper alignment until the final welds are made"

Any size weld that meets this definition is sufficient. The responsible engineer / supervisor should define the actual number. 30 mm, which is approximately 1" is a good number for large structures. For pipe welds 1/4" at several locations is usually enough. The size should be based on your experience with similar parts.